1. Field of the Invention
The present invention relates to an optical memory head for writing a large amount of information on an optical recording medium and reading a large amount of information from an optical recording medium and a magneto-optic recording medium by a vertical cavity surface emitting laser (VCSEL) array in an optical memory disk apparatus.
2. Description of Related Art
A conventional optical memory head in a magneto-optic writing apparatus forms a beam spot by focusing a laser emitted by a laser diode, i.e., a semiconductor laser, upon oscillation by using an optical focusing element such as a lens, and irradiates the beam spot on a ROM disk such as a CD (compact disk) or a DVD (digital versatile or video disk), an optical recording medium, or a magneto-optic recording medium. The head also may detect the reflecting light, thereby reading or writing information. A writing density of around 10.sup.7 to 10.sup.8 bit/cm.sup.2 has been realized by forming a fine beam spot having a diameter of about 1 .mu.m.
The optical memory head detects the header information of the optical recording medium or the reflecting light (tracking signal) reflected by a tracking guide formed on the medium, and is tracking-controlled by an actuator (device for moving the beam position) in order of 0.1 .mu.m. In this case, one laser diode or the like is used for writing/reading most frequently. There has been an attempt to use a single vertical cavity surface emitting laser in an optical memory disk writing/reading apparatus. However, this has not proven practical because it has only recently been developed and is very expensive.
Most of conventional optical memory disk writing/reading apparatuses use the floating head system in which the head does not contact the optical recording medium. No apparatus uses the contact head system in which the optical memory head writes and reads out data in contact with the optical recording medium via a lubricant.
The conventional optical memory disk writing/reading apparatus can write a larger amount of information on the optical recording medium or the like as the diameter of the beam stop is smaller. However, since its optical memory head complies with conventional classic geometrical optic principles involved in using an optical focusing element, a laser beam can only be focused on a spot size up to a diameter about equal to the used light wavelength or about a fraction thereof due to diffraction limited restriction of the light wave-length. Even in an optical recording medium 120 mm in diameter which is frequently used, a recording capacity of 10 GB can be ensured at most. For this reason, the appearance of an epochal optical memory head capable of ensuring a larger recording capacity is desired to strongly support the rapid technical advance in memory storage and the like in today's multimedia communications.